MTU Size on Tunnel Interface

MTU Size on Tunnel Interface

We have our MTU Size on our Tunnel Interfaces set at 1500 but the counters for NetFlow analzer are not counting up. If we lower the MTU size to 1300, the counters for the Tunnel Interface counts correctly. But when we lower the MTU size on the Tunnels we cannot get to every website with a DF (don't fragment) bit set. How can we get the router to export correctly...is it our version of Netflow, we are currently exporting version 5, do we need to export version 7 or where do we go to get correct utilization in our program. Please advise

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